Neuropsychiatric disorders such as schizophrenia, bipolar disorder (BD), and autism spectrum disorders (ASD) are multifactorial disorders caused by genetic and environmental influences. Although the genetic contribution is large, patient genetic studies have been fraught with weak, inconsistent results that have stalled research into the neurobiological mechanisms of these disorders. Recent genome-wide association studies (GWAS) using large patient populations have ignited the field by identifying several risk genes with high statistical confidence in multiple studies. Biological investigation in cellular and animl model systems is critical to define the function of these genes in disease. However, animal studies are constrained by technological limitations rendering it technically difficult to perform functional genetic studies in the mammalian brain using conventional molecular approaches. Ankyrin 3 (ANK3) is among the strongest and most replicated genes identified by multiple GWAS of BD. While it is known than ANK3 encodes the critical scaffold protein ankyrin G, the mechanism through which it contributes to BD remains completely unknown. Further, the complexity of the ANK3 genomic structure, comprised of ~20 known alternatively spliced transcript variants spanning several hundreds of kilobases of sequence, greatly complicates studies of its mechanism in disease. This proposal will investigate ANK3 in the regulation of mood-related behavior in mice to understand its disease mechanism. To overcome the challenge of studying large genes such as ANK3 in the brain, we propose a proof-of-concept study to develop a novel isoform-specific transcriptional modulation technology using designer transcription activator-like effectors (TALEs). TALEs are naturally occurring DNA binding proteins that we have recently developed as a generalizable platform for anchoring effector domains to specific locations on the mammalian genome. Using this technology, we will engineer novel TALEs to modulate the transcription level of different mouse ANK3 transcript variants within specific brain circuits implicated in mood and BD, and study their circuit- specifi contribution to mood-related behaviors. By coupling this novel transcription modulation technology with well-established genetic and behavioral analysis of ANK3 mouse models in our laboratory, we aim to establish the causal relationship between neural aberrations and altered transcriptional states of specific ANK3 transcript variants. Results from our studies will help advance our current understanding of the role of ANK3 in brain function and has the potential to establish completely novel BD therapeutic targets. While this proposal focuses on ANK3, it will also serve as a proof-of-concept study to establish novel isoform-specific TALE technology as a general strategy that will have broad applications across molecular neuroscience.